OK, let's consider your view point. Perhaps England had lions a few thousand years ago, they went extinct and perhaps some other predator took its place or may be it didn't, maybe the predator that was above it (if there was one) in the food chain went extinct too. But, yeah human life went on.

Now, here's where I disagree. The effects of extinction perhaps seem more pronounced with some species, rather than others. For instance, take coral reefs and how these could trigger a cascade of events affecting a bunch of species like small fish all the way up to human industry and life. Same with say bees, where they potentially can affect agriculture and humans in a huge way considering they are instrumental for pollination.

I suppose people don't like the idea of incurring the cost of efforts to prevent a species from extinction when they think its simply a moral thing to do, but in reality I suppose everything from climate change to saving endangered species is all just an effort towards self preservation for humans, perhaps simply branded differently.